One of the symptoms of ophthalmic diseases drawing much attention these days is dry eye. The dry eye is defined to mean a condition wherein lacrimal fluid is less in amount or abnormal in quality, with or without the presence of corneal and conjunctival lesion (Yamada, M. et al., Folia Ophthalmol. Jpn., 43, 1289-1293 (1992)). Specific symptoms include dry eye observed in hypolacrimation, alacrima, xerophthalmia, Sjögren syndrome, keratoconjunctivitis sicca, Stevens-Johnson syndrome, ocular pemphigoid, marginal blepharitis, diabetes and the like, dry eye observed after cataract operation, dry eye in conjunction with allergic conjunctivitis and the like, and dry eye due to hypolacrimation caused by increased VDT (visual display terminal) work, dry room with air conditioning and the like.
The dry eye is caused by various factors that may not be entirely clear, and, at the moment, a drastic treatment method, such as promotion of the secretion of lacrimal fluid, has not been established yet. Therefore, the dry eye has been diagnosed according to the subjective symptoms obtained by questioning and objective symptoms known from lacrimal fluid evaluation tests (tear film breakup time, Schirmer test, lacrimal fluid clearance test and the like), corneal and conjunctival staining tests (fluorescein staining, rose bengale staining and the like), and the like. For example, tear film breakup time (BUT), which is one of the lacrimal fluid evaluation tests, reflects the stability of precorneal tear film, and means the time (sec) from complete nictitation to the initial breakage of the precorneal tear film. A lower BUT means severer dry eye symptom. In the case of severe dry eye, the breakage of the tear film occurs immediately after nictitation, which is rated as BUT zero (0) sec.
At present, a dry eye therapy includes increasing lacrimal fluid reservoir in conjunctival sac by instillation of artificial tears to alleviate the subjective symptoms of patients or to protect the eye from drying, and other methods.
For the above-mentioned therapy, instillation of chondroitin sulfate, methyl cellulose and the like, and internal use of bromhexine hydrochloride, salivary gland hormone and the like have been the typical methods. However, the effect of such therapy is not necessarily satisfactory. While instillation of artificial tears and use of a goggle eye patch and the like have been the means to protect the eyes from drying, these are not more than auxiliary therapy methods.